Memory system having point-to-point (ptp) and point-to-two-point (pttp) links between devices

ABSTRACT

A memory system has first and second primary memories and first and second secondary memories coupled to the first and second primary memories, respectively, the coupling comprising at least one point-to-point connection. A memory module includes at least two of the first and second primary and first and second secondary memories. A first connection element, such as a connector or solder, connects the memory module to a mother board. A second connection element, such as a connector or solder, connects at least one other of the first and second primary and first and second secondary memories to the mother board. At least one of the memories on the first memory module is coupled to at least one of the other memories. The memory system also includes a memory controller which is connected to the primary memories by a point-to-two-point link.

RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.11/603,648, filed Nov. 22, 2006, which relies for priority on KoreanPatent Application number 2005-0120882, filed on Dec. 9, 2005, in theKorean Intellectual Property Office and Korean Patent Application number2006-0005103, filed on Jan. 17, 2006, in the Korean IntellectualProperty Office, the contents of which applications are incorporatedherein in their entirety by reference.

FIELD OF THE INVENTION

The invention relates to a memory system and more particularly, to amemory system having a point-to-point (PTP) link structure betweenmemory devices.

BACKGROUND OF THE INVENTION

FIG. 1 contains a block diagram of a conventional memory system 10having a plurality of memory devices M0-Mm, e.g., m=7, on a plurality ofmemory modules MM0-MMn, 14, 12, connected to a controller 16. The numberm of memory devices M0-Mm on each memory module MM0-MMn is determinedwith respect to the system bus width. For example, if the system buswidth is ×64 and the memory devices have a ×8 DQ bus, each memory moduleMM0-MMn has eight memory devices M0-M7. Data signal lines DQ0-7,DQ8-15,. . . , DQ56-63 have multi-drop links, such that the memorydevices share the data signal lines. The capacitive load of the datalines affects the operation speed of the memory system. For example, 8SDRAM, 4DDR (double data rate), 2DDR2 and 2DDR3 operationalconfigurations typically may be connected together to respective datasignal lines. As the operating speed of such systems increases, itbecomes important to reduce capacitive loading of the data signal linesto avoid the degradation of operation speed introduced by the capacitiveloading.

The command/address (C/A) signal lines C/A0 and C/A1 have multi-droplinks, so that memory devices M0-Mm on the same module MM0-MMn share thesame C/A signal line. In general, 8 or 4 memory devices share a singleC/A line, depending on the system bus speed. For higher bus speeds, 8memory devices typically share a common C/A line.

At present, the speed of a C/A line is slower than that of a data DQline because of the loading effects. For DDR operation, the C/A bus isbeing operated at single data rate (SDR), half of the DQ speed. Forhigher speed operation, it will also be important to reduce capacitiveloading and stub of the C/A line.

For a high-speed memory system, i.e., a system operating at more than 2Gbps, a point-to-point (PTP) link, as opposed to a multi-drop link,between memory devices and between the controller and memory devices hasbeen studied to reduce capacitive loading and stub of each signal lineto meet high-speed operational requirements. For a high-density memorysystem supporting the PTP link, a plurality of memory modules are neededto support the memory application such as server or networking, but eachmemory module comprising the PTP link should have an input/output I/Omodule tab for each signal line. This causes an increase in the numberof tabs, making it difficult to design and produce a suitable memorymodule. An approach in a high-density memory system supporting PTPwithout increasing the number of module tabs is to use stacked memorieson a single memory module.

If stacked memories mounted on one memory module are adopted, someproblems are expected. For example, the thermal management between anupper memory and a lower memory would be a difficult issue to resolve.Also, signal routing between an upper memory and a lower memory wouldbecome very complex and difficult to implement, and can lead to anincrease in memory package size. Also, it would be difficult to increasethe density of the memory system while maintaining the PTP link.

SUMMARY OF THE INVENTION

The present invention is directed to an approach to providing a memorysystem having a point-to-two-point (referred to herein as “1P2P”) linkfor merged write data and command/address (WR/CA) signal lines and apoint-to-point (referred to herein as “1P1P”) link for read data (DQ)signal lines.

The present invention provides a memory package capable of supporting aPTP link without an increase in memory package size. The presentinvention also provides a memory system having a PTP link among memorydevices. These features are provided without increasing the number ofconnector pins in the memory module.

According to a first aspect, the invention is directed to a memorysystem, comprising first and second primary memories and first andsecond secondary memories coupled to the first and second primarymemories, respectively, the coupling comprising at least onepoint-to-point connection. At least one memory module has at least twoof the first and second primary and first and second secondary memories.A first connection element connects the memory module to a mother board.A second connection element connects at least one other of the first andsecond primary and first and second secondary memories to the motherboard. At least one of the memories on the first memory module iscoupled to at least one of the other memories.

In one embodiment, the first connection element is a connectorconnecting the memory module to the mother board.

In one embodiment, the second connection element comprises solder forfixedly attaching the at least one other of the first and second primaryand first and second secondary memories to the mother board.

In one embodiment, the first primary memory and the second primarymemory are affixed to the first memory module.

In one embodiment, the first primary memory and the first secondarymemory are affixed to the first memory module.

In one embodiment, the first primary memory and the second primarymemory are soldered to the mother board.

In one embodiment, the first primary memory and the first secondarymemory are soldered to the mother board.

The memory system can further include a second memory module to which atleast two others of the first and second primary and first and secondsecondary memories are attached. The second connection element can be aconnector connecting the second memory module to the mother board. Aflexible conductor element can connect the first and second memorymodules. The flexible conductor element can carry command/address (CA)signals and/or data signals. The first primary memory and the secondprimary memory can be affixed to the first memory module. The firstprimary memory and the first secondary memory can be affixed to thefirst memory module. The first secondary memory and the second secondarymemory can be affixed to the second memory module. The second primarymemory and the second secondary memory can be affixed to the secondmemory module.

The memory system can further include a controller coupled to at leastone of the first and second primary memories. The controller can becoupled to the at least one primary memory via a point-to-point link.The controller can be coupled to the first and second primary memoriesvia a point-to-two-point link. The controller can transmitcommand/address (CA) signals to both of the primary memories. In oneembodiment, during an access to one of the secondary memories, one ofthe primary memories repeats command/address signals from the controllerto the one of the secondary memories being accessed. In one embodiment,a first half of data being accessed is transferred to the controller byone of the primary and secondary memories, and a second half of the databeing accessed is transferred to the controller by another of theprimary and secondary memories. In one embodiment, a first half of databeing accessed is transferred to the controller by one of the secondarymemories, and a second half of the data being accessed is transferred tothe controller the other of the secondary memories.

According to another aspect, the invention is directed to a memorysystem comprising first and second primary memories and a controller fortransmitting signals to the first and second primary memories, thesignals being transmitted to the first and second memories by apoint-to-two-point link.

In one embodiment, the signals comprise command/address (CA) signals.First and second secondary memories can be coupled to the first andsecond primary memories, respectively. Coupling between the primary andsecondary memories can include at lest one point-to-point connection.The memory system can further include a first memory module having atleast two of the first and second primary and first and second secondarymemories and a second memory module having at least the other two of thefirst and second primary and fist and second secondary memories.

A flexible conductor element may connect the first and second memorymodules. The flexible conductor element can carry command/address (CA)signals and/or data signals.

In one embodiment, the controller transmits command/address (CA) signalsto both of the primary memories. In one embodiment, during an access toone of the secondary memories, one of the primary memories repeatscommand/address (CA) signals from the controller to the one of thesecondary memories being accessed. A first half of data being accessedcan be transferred to the controller by one of the primary and secondarymemories, and a second half of the data being accessed is transferred tothe controller by another of the primary and secondary memories. A firsthalf of data being accessed can be transferred to the controller by oneof the secondary memories, and a second half of the data being accessedis transferred to the controller the other of the secondary memories.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features and advantages of theinvention will be apparent from the more particular description ofpreferred aspects of the invention, as illustrated in the accompanyingdrawings in which like reference characters refer to the same partsthroughout the different views. The drawings are not necessarily toscale, emphasis instead being placed upon illustrating the principles ofthe invention. In the drawings, the thickness of layers and regions areexaggerated for clarity.

FIG. 1 contains a block diagram of a conventional memory system having aplurality of memory devices on a plurality of memory modules.

FIG. 2A contains a schematic block diagram of a memory system inaccordance with an embodiment of the invention.

FIG. 2B contains a schematic diagram illustrating the configurations ofthe links in the memory system of FIG. 2A.

FIGS. 3A and 3B contain timing diagrams illustrating the timing of aread operation in accordance with the embodiment of the inventionillustrated in FIG. 2A.

FIG. 4A is a schematic block diagram of a memory system in accordancewith another embodiment of the invention.

FIG. 4B contains a schematic diagram illustrating the configurations ofthe links in the memory system 200 of FIG. 4A.

FIG. 5 is a schematic diagram of the memory system of FIG. 4A,illustrating the physical configuration of the memory system.

FIG. 6A is a schematic block diagram of a memory system in accordancewith another embodiment of the invention.

FIG. 6B contains a schematic diagram illustrating the configurations ofthe links in the memory system of FIG. 6A.

FIG. 7 is a schematic diagram of the memory system of FIG. 6A,illustrating the physical configuration of the memory system.

FIG. 8A is a schematic block diagram of a memory system in accordancewith another embodiment of the invention.

FIG. 8B contains a schematic diagram illustrating the configurations ofthe links in the memory system of FIG. 8A.

FIG. 9 is a schematic diagram of the memory system of FIG. 8A,illustrating the physical configuration of the memory system.

FIGS. 10A and 10B contain timing diagrams of a read operation for theembodiment of the invention illustrated in FIGS. 8A and 9.

FIG. 11 is a schematic block diagram of a memory system in accordancewith another embodiment of the invention.

FIG. 12 is a schematic diagram of the memory system of FIG. 11,illustrating the physical configuration of the memory system.

FIG. 13A is a schematic block diagram of a memory system in accordancewith another embodiment of the invention.

FIG. 13B contains a schematic diagram illustrating the configurations ofthe links in the memory system of FIG. 13A.

FIGS. 14A and 14B contain timing diagrams of a read operation for theembodiment of the invention illustrated in FIG. 13A.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

FIG. 2A contains a schematic block diagram of a memory system 100 inaccordance with an embodiment of the invention. The memory system 100 ofFIG. 2A includes a memory controller 120 and two memory modules 114(MM0) and 112 (MM1). In this case, the memory link to the controller isdivided into the two separate memory modules MM0, MM1, rather than asingle memory module. Each of the memory modules MM0, MM1 includes agroup of primary (P) memories 116, 122 connected to a respective groupof secondary (S) memories 118, 124 in the same planar structure. WR/CAsignal lines are connected from a transmitting port TP of the controller120 to the primary memories 116, 122. In this embodiment, the WR/CAsignals are merged write data signals and command/address signals. Thatis, command/address signals and write data signals share the WR/CAsignal lines. Read data signals RD1, RD2 are connected from thesecondary memories 118, 124, respectively, to receiving ports RP1, RP2,respectively, of the controller 120.

Each of the primary (P) and secondary (S) memories includes a pluralityof ports. In the illustrated embodiment, each of the primary (P)memories includes a receive-from-controller (RFC) port, atransmit-to-memory (TTD) port and a transmit-to-controller (TTC) port.Each of the secondary (S) memories includes a receive-from-controller(RFC) port, a receive-from-memory (RFD) port and atransmit-to-controller (TTC) port. In the primary (P) memories, the RFCport receives WR/CA signals from the controller 120; the TTD porttransfers WR/CA signals to the connected secondary (S) memory; and theTTC port transmits primary memory read data to the secondary (S) memory.In the secondary (S) memories, the RFC port receives WR/CA signals fromthe connected primary (P) memory; the RFD port receives primary memoryread data from the connected primary memory; and the TTC port transmitssecondary memory read data or primary read data from the connectedprimary memory to the controller 120.

In this embodiment, the link from the transmitting port TP of thecontroller 120 transmits WR/CA signals to the primary memories 116, 122via a point-to-two-point (PTTP or 1P2P) link, meaning that the WR/CAsignal lines are simultaneously connected from the TP port of thecontroller to both of the two RFC ports of the primary memories 116,122. In this embodiment, the links from the secondary memories 118, 124are point-to-point (PTP or 1P1P) links.

WR/CA signals for a primary memory access are transmitted to the primarymemories 116, 122 via the PTTP (1P2P) link of the invention. In the caseof a primary read operation, read data is transmitted by the primarymemory 116, 122 out of the TTC port to the connected secondary memory118, 124. The secondary memory 118, 124 then transmits or repeats theprimary read data to the controller 120 out of the TTC port of thesecondary memory 118, 124 via the PTP link. In the case of a secondarymemory access, WR/CA signals are transmitted to the primary memories116, 122 via the PTTP (1P2P) link of the invention. The WR/CA signalsare transferred or repeated to the secondary memories 118, 124 via theTTD port of the primary memories 116, 122 and the RFC port of thesecondary memories 118, 124. In the case of a secondary memory readoperation, the read data is transmitted to the controller 120 out of theTTC port of the secondary memory 118, 124 via the PTP (1P1P) link.

As noted above, in this embodiment, the memory link to the controller isdivided into the two separate memory modules MM0, MM1, rather than asingle memory module. The PTTP (1P2P) link for the WR/CA signalsprovides for the WR/CA signals to be transmitted to both primarymemories 116, 122 simultaneously. Also, according to this embodiment, ifread data is M bits, each secondary memory 118, 124 provides half of thedata, i.e., M/2 bits, to the controller 120. That is, the read data RD1transmitted from the secondary memory 118 to the receive port RP1 of thecontroller 120 is M/2 bits. The read data RD2 transmitted from thesecondary memory 124 to the receive port RP2 of the controller 120 isalso M/2 bits.

FIG. 2B contains a schematic diagram illustrating the configurations ofthe links in the memory system 100 of FIG. 2A. As indicated in thediagram of FIG. 2B, a PTTP link connects the transmitting port TP to twoprimary memories P (116, 122), and PTP links connect each of the primarymemories P (116, 122) to a corresponding secondary memory S (118, 124).PTP links connect each primary memory P (116, 122) to a correspondingsecondary memory S (118, 124) and to a corresponding receiving port RP1,RP2.

FIGS. 3A and 3B contain timing diagrams illustrating the timing of aread operation in accordance with the embodiment of the inventionillustrated in FIG. 2. Specifically, FIG. 3A illustrates the timing of aread operation performed on a primary (P) memory 116, 122, and FIG. 3Billustrates the timing of a read operation performed on a secondary (S)memory 118, 124.

Referring to FIG. 3A, the primary memories 116, 122 of the memorymodules MM0, MM1 (MM0 P and MM1 P) operate simultaneously in response tothe primary read command (RDP), such that each primary memory outputshalf of the requested data RD1 and RD2 to the respective secondarymemories 118, 124 after a predetermined read latency. The requested dataRD1 and RD2 is repeated by respective secondary memories 118, 124 to thecontroller 120.

Referring to FIG. 3B, the secondary memories 118, 124 of the memorymodules MM0, MM1 (MM0 S and MM1 S) operate simultaneously in response tothe secondary read command (RDS) which is received from the respectiveprimary memories 116, 122 after a repeating delay. Then each secondarymemory outputs half of the requested data RD1 and RD2 to the controller120 after the predetermined read latency. As noted in both FIGS. 3A and3B in the cases of both a primary read and a secondary read, all of theread data is available to the controller at the same time, with readlatency and repeating delay, even in the case of dividing the memoryinto two memory modules MM0, MM1, according to the invention.

FIG. 4A is a schematic block diagram of a memory system 200 inaccordance with another embodiment of the invention. FIG. 5 is aschematic diagram of the memory system 200 of FIG. 4A, illustrating thephysical configuration of the memory system 200.

Referring to FIGS. 4A and 5, the memory system 200 includes a pair ofmemory modules 214 (MM0) and 212 (MM1) connected at lower conductivetabs 236 and 230, respectively, to a mother board 242 at connectors 246and 244, respectively, on the mother board 242. Two primary memories216, 222 (P1, P2) are mounted on module MM0, and two secondary memories218, 224 (S1, S2) are mounted on module MM1. The RFC ports of primarymemories P1 and P2 are connected together via printed circuit wiring onthe module MM0 circuit board. The primary memories P1 and P2 areconnected to the secondary memories S1 and S2 via a flexible cable 240having printed conductors connected between the upper tabs 232 of themodule MM1 and the upper tabs 234 of the module MM0.

In the embodiment of FIGS. 4A and 5, the logical connections among theprimary memories, the secondary memories and the controller 220 are thesame as those of the embodiment of FIG. 2A. That is, the embodiment ofFIGS. 4A and 5 implements the memory system functional operations asdescribed above in connection with the embodiment of FIG. 2A, includingbut not limited to the repeating of WR/CA signals from primary memory tosecondary memory and repeating of read data from a primary memory by asecondary memory to the controller. The WR/CA signals are transmitted atthe transmitting port TP by the controller 220 in a PTTP (1P2P) link toboth primary memories P1, P2. The signals being transferred from theprimary memories P1, P2 to the secondary memories S1, S2 are transmittedover the flexible cable 240 between the modules MM0, MM1. Read data RD1signals are transmitted via PTP (1P1P) link out of the TTC port of thesecondary memory S1 218 and are routed through the memory module MM1 onlines 241 to the lower tabs 230, through the connector 244 and to thereceiving port RP1 of the controller 220 through the mother board 242.Read data RD2 signals are transmitted via PTP (1P1P) link out of the TTCport of the secondary memory S2 224 and are routed through the memorymodule MM1 on lines 243 to the lower tabs 230, through the connector 244and to receiving port RP2 of the controller 220 through the mother board242.

FIG. 4B contains a schematic diagram illustrating the configurations ofthe links in the memory system 200 of FIG. 4A. As indicated in thediagram of FIG. 4B, a PTTP link connects the transmitting port TP to twoprimary memories P1 (216) and P2 (222), and PTP links connect each ofthe primary memories P1 (216) and P2 (222) to a corresponding secondarymemory S1 (218) and S2 (224). PTP links connect each primary memory P1(216) and P2 (222) to a corresponding secondary memory S1 (218) and S2(224) and to a corresponding receiving port RP1, RP2.

FIG. 6A is a schematic block diagram of a memory system 300 inaccordance with another embodiment of the invention. FIG. 7 is aschematic diagram of the memory system 300 of FIG. 6A, illustrating thephysical configuration of the memory system 300.

In the embodiment of FIGS. 6A and 7, the memory system 300 includes apair of memory modules 314 (MM0) and 312 (MM1) connected at lowerconductive tabs 336 and 330, respectively, to a mother board 342 atconnectors 346 and 344, respectively, on the mother board 342. A primarymemory 316 and a secondary memory 324 are mounted on module MM0, and aprimary memory 322 and a secondary memory 324 are mounted on module MM1.The primary memory 316 and the secondary memory 324 are connectedtogether via printed circuit wiring on the module MM0 circuit board, andthe primary memory 322 and the secondary memory 318 are connectedtogether via printed circuit wiring on the module MM1 circuit board. Theprimary memory 316 is connected to the primary memory 322 via a flexiblecable 340 having printed conductors connected between the upper tabs 332of the module MM1 and the upper tabs 334 of the module MM0.

In the embodiment of FIGS. 6A and 7, the logical connections among theprimary memories, the secondary memories and the controller 320 are thesame as those of the embodiment of FIG. 2A. That is, the embodiment ofFIGS. 6A and 7 implements the memory system functional operations asdescribed above in connection with the embodiment of FIG. 2A, includingbut not limited to the repeating of WR/CA signals from primary memory tosecondary memory and repeating of read data from a primary memory by asecondary memory to the controller. The WR/CA signals are transmitted atthe transmitting port TP by the controller 320 in a PTTP (1P2P) link toboth primary memories 316, 322. The signals being transferred from theprimary memory 316 to the secondary memory 324 are transferred oncircuit wiring printed on the memory module MM0, and the signals beingtransferred from the primary memory 322 to the secondary memory 318 aretransferred on circuit wiring printed on the memory module MM1. TheWR/CA signals in the PTTP link are transferred to the primary memory 322along the flexible cable 340. Read data RD1 signals are transmitted viaPTP (1P1P) link out of the TTC port of the secondary memory 324 and arerouted through the memory module MM0 on lines 343 through the connector346 to the receiving port RP1 of the controller 320 through the motherboard 342. Read data RD2 signals are transmitted via PTP (1P1P) link outof the TTC port of the secondary memory 318 and are routed through thememory module MM1 on lines 341 to the lower tabs 330, through theconnector 344 to receiving port RP2 of the controller 320 through themother board 342.

FIG. 6B contains a schematic diagram illustrating the configurations ofthe links in the memory system 300 of FIG. 6A. As indicated in thediagram of FIG. 6B, a PTTP link connects the transmitting port TP to twoprimary memories P (316, 322), and PTP links connect each of the primarymemories P (316, 322) to a corresponding secondary memory S (324, 318).PTP links connect each primary memory P (316, 322) to a correspondingsecondary memory S (324, 318) and to a corresponding receiving port RP1,RP2.

FIG. 8A is a schematic block diagram of a memory system 400 inaccordance with another embodiment of the invention. FIG. 9 is aschematic diagram of the memory system 400 of FIG. 8A, illustrating thephysical configuration of the memory system 400.

In the embodiment of FIGS. 8A and 9, the memory system 400 includes asingle memory module 414 (MM0) connected at lower conductive tabs 432 toa mother board 442 at connector 446 on the mother board 442. A primarymemory (P1) 422 and a secondary memory (S1) 418 are mounted on moduleMM0, and a primary memory (P) 416 and a secondary memory (S) 424 arehard mounted such as by soldering on a soldering area 425 of the motherboard 442. The primary memory 416 and the secondary memory 424 areconnected together via printed circuit wiring on the mother board 442.The primary memory 422 and the secondary memory 418 are connectedtogether via printed circuit wiring on the module MM0 circuit board. Theprimary memory 416 is connected to the primary memory 422 via printedcircuit wiring on the mother board 442 through the connector 446,through the circuit board of the memory module 414. The secondary memory424 is connected to the secondary memory 418 via printed circuit wiringon the mother board 442 through the connector 446, through the circuitboard of the memory module 414.

In the embodiment of FIGS. 8A and 9, the logical connections among theprimary memories, the secondary memories and the controller 420 are thesame as those of the embodiment of FIG. 2A. That is, the embodiment ofFIGS. 8A and 9 implements the memory system functional operations asdescribed above in connection with the embodiment of FIG. 2A, includingbut not limited to the repeating of WR/CA signals from primary memory tosecondary memory and repeating of read data from a primary memory by asecondary memory to the controller. The WR/CA signals are transmitted atthe transmitting port TP by the controller 420 in a PTTP (1P2P) link toboth primary memories 416, 422. The signals being transferred from theprimary memory 416 to the secondary memory 424 are transferred oncircuit wiring printed on the mother board 420, and the signals beingtransferred from the primary memory 422 to the secondary memory 418 aretransferred on circuit wiring printed on the memory module MM0. TheWR/CA signals in the PTTP link are transferred to the primary memory 422along circuit wiring printed on the mother board 442, through theconnector 446 and circuit wiring printed on the circuit board of thememory module MM0. The WR/CA signals in the PTTP link are transferred tothe primary memory 416 along circuit wiring printed on the mother board442. Read data RD1 signals are transmitted via PTP (1P1P) link out ofthe TTC port of the primary memory 416 and are routed through the motherboard 442 on lines 443 to the receiving port RP1 of the controller 420.Read data RD2 signals are transmitted out of the TTC port of thesecondary memory 424 and are routed through the mother board 442 onlines 441 to receiving port RP2 of the controller 420.

It should be noted that, in the embodiment of FIGS. 8A and 9, thememories on the mother board 442 have shorter read paths that thememories on the memory module MM0. As a result, the read latency of thememories on the mother board 442 may be set to be longer than that ofthe memories on the memory module MM0 such that the read data isreceived at the controller 420 at or about the same time.

FIG. 8B contains a schematic diagram illustrating the configurations ofthe links in the memory system 400 of FIG. 8A. As indicated in thediagram of FIG. 8B, a PTTP link connects the transmitting port TP to twoprimary memories P (416) and P1 (422), and PTP links connect each of theprimary memories P (416) and P1 (422) to a corresponding secondarymemory S (424) and S1 (418). PTP links connect the primary memory P1(422) to the primary memory P (416) to the corresponding receiving portRP1. PTP links connect the secondary memory S1 (418) to the secondarymemory S (424) to the corresponding receiving port RP2.

FIGS. 10A and 10B contain timing diagrams of a read operation for theembodiment of the invention illustrated in FIGS. 8A and 9. Specifically,FIG. 10A illustrates the timing of a read operation (RD) performed onthe primary (P) memory 416 and the secondary (S) memory 424 on themother board 442, and FIG. 10B illustrates the timing of a readoperation MM0 RD performed on the primary (P1) memory 422 and thesecondary (S1) memory 418 on the memory module MM0.

Referring to FIG. 10A, the primary memory 416 receives the RD andrepeats the RD1 to the secondary memory 424 after the repeating delay.The primary memory 416 reads out RD1 after a predetermined read latency1 and the secondary memory 424 S reads out RD2 after a predeterminedread latency 2. To receive the read data RD1 and RD2 at the controller420 at or about the same time, The primary memory has a longer readlatency 1 than the read latency 2 of the secondary memory. Referring toFIG. 10B, the primary memory P1 receives the read command MM0 RD andrepeats it to the secondary memory S1 after a repeating delay. Theprimary memory P1 reads out the RD1 to the primary memory P after readlatency 1. The secondary memory S1 reads out the RD2 to the secondarymemory S after read latency 2. P and S repeats the RD1 and RD2respectively to the controller. The controller receives the RD1 and RD2after the repeating delay.

In terms of signal flow, referring to FIGS. 8A, 8B, 9, 10A and 10B,WR/CA signals from the controller 420 are sent to primary memories P andP1. Primary memory P repeats the WR/CA signals to the secondary memoryS, and primary memory P1 repeats the WR/CA signals to the secondarymemory S1. In the case of reading data from primary memory P, read dataRD1 is read out of primary memory P and sent to the controller 420. Inthe case of reading data from P1, read data RD1 is transferred toprimary memory P, which repeats the read data RD1 to the controller 420.In the case of reading the secondary memory S, after the WR/CA signalsare repeated to S by P, the read data RD2 is read from S and transferredto the controller 420. In the case of reading the secondary memory S1,after the WR/CA signals are repeated to S1 by P1, the read data RD2 isread from S1 and transferred to S. The read data is then repeated to thecontroller 420.

As noted in both FIGS. 10A and 10B, in the cases of both a read of themother board memories and the module memories, all of the read data isavailable to the controller 420 at the same time, even in the case ofdividing the memory into a memory module MM0 and mother board memories,according to the invention.

FIG. 11 is a schematic block diagram of a memory system 500 inaccordance with another embodiment of the invention. FIG. 12 is aschematic diagram of the memory system 500 of FIG. 11, illustrating thephysical configuration of the memory system 500.

In the embodiment of FIGS. 11 and 12, the memory system 500 includes asingle memory modules 514 (MM0) connected at lower conductive tabs 532to a mother board 542 at connector 546 on the mother board 542. Asecondary memory (S1) 518 and a secondary memory (S2) 524 are mounted onmodule MM0, and a primary memory (P1) 516 and a primary memory (P2) 522are hard mounted such as by soldering on a soldering area 525 of themother board 542. The primary memory P1 516 is connected to thesecondary memory S1 518 via printed circuit wiring on the mother board542 through the connector 546, through the circuit board of the memorymodule 514. The primary memory P2 522 is connected to the secondarymemory S2 524 via printed circuit wiring on the mother board 542 throughthe connector 546, through the circuit board of the memory module 514.

In the embodiment of FIGS. 11 and 12, the logical connections among theprimary memories, the secondary memories and the controller 520 are thesame as those of the embodiment of FIG. 2A. That is, the embodiment ofFIGS. 11 and 12 implements the memory system functional operations asdescribed above in connection with the embodiment of FIG. 2A, includingbut not limited to the repeating of WR/CA signals from primary memory tosecondary memory and repeating of read data from a primary memory by asecondary memory to the controller. The WR/CA signals are transmitted atthe transmitting port TP by the controller 520 in a PTTP (1P2P) link toboth primary memories 516, 522. The signals being transferred from theprimary memory 516 to the primary memory 522 are transferred on circuitwiring printed on the mother board 542, and the signals beingtransferred from the secondary memory 518 to the secondary memory 524are transferred on circuit wiring printed on the memory module MM0. TheWR/CA signals in the PTTP link are transferred to the primary memories516 and 522 along circuit wiring printed on the mother board 542. Readdata RD1 signals are transmitted via PTP (1P1P) link out of the TTC portof the primary memory 516 and are routed through the mother board 542 onlines 543 to the receiving port RP1 of the controller 520. Read data RD2signals are transmitted out of the TTC port of the primary memory 522and are routed through the mother board 542 on lines 541 to receivingport RP2 of the controller 420.

In terms of signal flow, referring to FIGS. 11 and 12, WR/CA signalsfrom the controller 520 are sent to primary memories P1 and P2. Then PIrepeats the WR/CA signals to the secondary memory S1, and secondarymemory SI repeats the WR/CA signals to the secondary memory S2. In thecase of reading data from primary memories, read data RD1 and RD2 areoutput from P1 and P2 to the controller 520. In the case of reading datafrom secondary memories S1 and S2, read data RD1 and RD2 are output fromS1 and S2 to primary memories P1 and P2, respectively, and then arerepeated by P1 and P2 to transfer RD1 and RD2 to the controller 520.

The primary memory 516 is connected to the secondary memory 518 vialines 547, 549 printed on the mother board 542, passing through theconnector 546 and through the circuit board on the memory module MM0.The primary memory 522 is connected to the secondary memory 524 vialines 545 printed on the mother board 542, passing through the connector546 and through the circuit board on the memory module MM0.

It should be noted that, in the embodiment of FIGS. 11 and 12, thememories on the mother board 542 have shorter read paths that thememories on the memory module MM0. As a result, the read latency of thememories on the mother board 542 may be set to be longer than that ofthe memories on the memory module MM0 such that the read data isreceived at the controller 520 at or about the same time.

FIG. 13A is a schematic block diagram of a memory system 600 inaccordance with another embodiment of the invention. The memory system600 is the same as that of FIGS. 11 and 12, except that an additionalset of secondary memories 518 a and 518 b is included on a second memorymodule MM1 514 a. In FIG. 13A, like reference numerals refer to likeelements in FIGS. 11 and 12. As indicated in the diagram of FIG. 13B, aPTTP link connects the transmitting port TP to primary memories P1 andP2, and PTP links connect P1 and P2 to S1 (518, 518 a) and S2 (524, 524a). PTP links connect S1 (518 a) to S1 (518) to P1 to the receiving portRP 1. PTP links connect S2 (524 a) to S2 (524) to P2 to the receivingport RP2. In accordance with the invention, in general, any number ofsecondary memories can be added in like fashion to that shown in FIG.13. This allows for the expansion of memory density while maintainingthe PTTP (1P2P) WR/CA links and the PTP (1P2P) read data links.

FIGS. 14A and 14B contain timing diagrams of a read operation for theembodiment of the invention illustrated in FIG. 13A. Specifically, FIG.14A illustrates the timing of a read operation (RD) performed on memorymodule MM0, and FIG. 14B illustrates the timing of a read operation (MM1RD) performed on memory module MM1.

Referring to FIG. 14A, the primary memory P1 and secondary memory S1operate simultaneously in response to the read command MM0 RD, such thatP1 outputs half of read data RD1 after read latency 1, and S1 outputshalf of the data RD2 after repeating delay and read latency 2. Also, inthe read operation of MM1, half of the read data RD1 is output afterthree repeating delays and read latency 4, and half of the read data RD2is output after two repeating delays and read latency 3.

In all of the embodiments described herein, PTTP link or PTP link forWR/CA and RD1 and RD2 may be one of single-ended signaling anddifferential signaling. Differential signaling would be used in the caseof high-speed operation. In the case of differential signaling, thenumber of pins used on the memory devices and modules would have to bemodified to accommodate the increased number of connections.

While the present invention has been particularly shown and describedwith reference to exemplary embodiments thereof, it will be understoodby those of ordinary skill in the art that various changes in form anddetails may be made therein without departing from the spirit and scopeof the present invention as defined by the following claims.

1. A memory system, comprising: a controller transmitting controlsignals; first and second primary memories receiving the control signalsfrom the controller via a point-to-two-point connection; and first andsecond secondary memories coupled to the first and second primarymemories, respectively, for receiving the control signals, the couplingcomprising at least one point-to-point connection, wherein each of twomemories of the first and second primary memories and the first and thesecond secondary memories transmits read data signals to the controllervia another point-to-point connection.
 2. The memory system of claim 1,further comprising: a first memory module having the first primarymemory and the first secondary memory coupled to the first primarymemory; and a second memory module having the second primary memory andthe second secondary memory coupled to the second primary memory,wherein each of the first and second secondary memories transmits theread data signals to the controller via the point-to-point connection.3. The memory system of claim 1, wherein, during an access to the firstand second secondary memories, the first and second primary memoriesrepeat the control signals from the controller to the first and secondsecondary memories being accessed.
 4. The memory system of claim 1,wherein a first half of the read data signals being accessed istransferred to the controller by the first secondary memory, and asecond half of the read data signals being accessed is transferred tothe controller by the second secondary memory.
 5. The memory system ofclaim 1, further comprising: a first memory module having the first andsecond primary memories; a second memory module having the first andsecond secondary memories; and a flexible cable having a firstconnection connecting between the first memory module and the secondmemory module, wherein the first and second secondary memories receivethe control signals through the first connection and each of the firstand second secondary memories transmits the read data signals to thecontroller via the point-to-point connection.
 6. The memory system ofclaim 5, wherein the controller further transmits write signals and theread data signals of first and second primary memories through the firstconnection.
 7. The memory system of claim 5, further comprising a secondconnection connecting between each of the first and second secondarymemories and the controller to transmit the read data signals of thefirst and second secondary memories.
 8. The memory system of claim 5,wherein, during an access to the first and second secondary memories,the first and second primary memories repeat the control signals fromthe controller to the first and second secondary memories beingaccessed.
 9. The memory system of claim 7, wherein a first half of theread data signals being accessed is transferred to the controllerthrough the second connection and a second half of the read data signalsbeing accessed is transferred to the controller through the secondconnection.
 10. The memory system of claim 2, further comprising: aflexible cable having a first connection connecting between the firstmemory module and the second memory module, wherein the second primarymemory receives the control signals from the controller through thefirst connection.
 11. The memory system of claim 10, wherein the firstand second secondary memories receive further write signals from thecontroller through the first connection.
 12. The memory system of claim10, further comprising a second connection connecting between the firstand second primary memories and the controller to transmit the controlsignals and a third connection connecting between each of the first andsecond secondary memories and the controller to transmit the read datasignals of the first and second secondary memories.
 13. The memorysystem of claim 10, wherein, during an access to the first and secondsecondary memories, the first and second primary memories repeat thecontrol signals from the controller to the first and second secondarymemories being accessed.
 14. The memory system of claim 10, wherein afirst half of the read data signals being accessed is transferred to thecontroller by the first secondary memory, and a second half of the readdata signals being accessed is transferred to the controller by thesecond secondary memory.
 15. The memory system of claim 1, furthercomprising: a first memory module having the first primary memory andthe first secondary memory receiving the control signals from the firstprimary memory, wherein the second primary memory and the secondsecondary memory are soldered on a mother board.
 16. The memory systemof claim 15, further comprising a second connection connecting betweenthe first primary memory and the second primary memory and between thefirst secondary memory and the second secondary memory; and a thirdconnection connecting between the second primary memory and thecontroller and between the second secondary memory and the controller,wherein the read data signals are transmitted through the secondconnection and the third connection.
 17. The memory system of claim 15,wherein the first primary memory and the first secondary memorysimultaneously operate and the second primary memory and the secondsecondary memory simultaneously operate.
 18. The memory system of claim15, wherein a read latency of the first and second primary memories islonger than that of the first and second secondary memories.
 19. Thememory system of claim 15, wherein, during an access to the first andsecond secondary memories, the first and second primary memories repeatthe control signals from the controller to the first and secondsecondary memories being accessed.
 20. The memory system of claim 15,wherein a first half of the read data signals being accessed isgenerated from the first primary memory and a second half of the readdata signals being accessed is generated from the first secondarymemory, or the first half of the read data signals being accessed isgenerated from the second primary memory and a second half of the readdata signals being accessed is generated from the second secondarymemory.
 21. The memory system of claim 1, further comprising: a firstmemory module having the first secondary memory receiving the controlsignals from the first primary memory and the second secondary memoryreceiving the control signals from the first secondary memory, whereinthe first and second primary memories are soldered on a mother board.22. The memory system of claim 21, wherein the controller furthertransmits write signals and the first and second primary memoriesfurther receive write data signals from the controller via thepoint-to-two-point connection.
 23. The memory system of claim 21,wherein the first primary memory and the first secondary memorysimultaneously operate and the second primary memory and the secondsecondary memory simultaneously operate.
 24. The memory system of claim21, wherein a first half of the read data signals being accessed isgenerated from the first primary memory and a second half of the readdata signals being accessed is generated from the first secondarymemory, or the first half of the read data signals being accessed isgenerated from the second primary memory and a second half of the readdata signals being accessed is generated from the second secondarymemory.
 25. The memory system of claim 21, further comprising: third andfourth secondary memories; a second memory module having the third andthe fourth secondary memories receiving the control signals from thesecond secondary memory via point-to-two-point connection.
 26. Thememory system of claim 25, wherein a first half of read data signalsbeing accessed is generated from the first primary memory and a secondhalf of the read data signals being accessed is generated from the firstsecondary memory, or the first half of the read data signals beingaccessed is generated from the second primary memory and a second halfof the read data signals being accessed is generated from the secondsecondary memory, or the first half of the read data signals beingaccessed is generated from the third secondary memory and the secondhalf of the read data signals being accessed is generated from thefourth secondary memory.
 27. A method for operating a memory system,comprising; transferring control signals to first and second primarymemories via a point-to-two-point connection; repeating the controlsignals from the first and second primary memories to first and secondsecondary memories, respectively, via a point-to-point connection; andtransferring read data signals from two of the first and the secondprimary memories and the first and the second secondary memories to acontroller via another point-to-point connection.
 28. The method ofclaim 27, wherein transferring the control signals further comprisestransferring write data signals to the first and second primary memoriesvia the point-to-two-point connection.